PGA1 and PGE1 have been shown to have a direct vasodilatory effect on regional vascular beds. Some investigators believe they are the principal mediators of coronary vasodilatation. Both drugs have been reported to increase coronary blood flow, heart rate, cardiac output, and dp/dt while decreasing mean aortic pressure and peripheral vascular resistance. These alleged actions of prostaglandins on the heart has prompted us to study their effect on cardiac hemodynamics and regional myocardial blood flow.